Selectin ligands: will the real ones please stand
up?
A Varki
J Clin Invest.
1997;
99(2)
:158-162.
https://doi.org/10.1172/JCI119142
.
Perspective
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© The American Society for Clinical Investigation, Inc. 0021-9738/97/01/158/05 $2.00
Volume 99, Number 2, January 1997, 158–162
Perspectives Series:
Cell Adhesion in Vascular Biology
Less than a decade ago, the cloning of three seemingly dispar-ate vascular cell surface molecules uncovered the selectin fam-ily of receptors that are now known to mediate critical cell-cell interactions in processes such as leukocyte trafficking, throm-bosis, acute and chronic inflammation, and ischemia-reperfu-sion injury (1–15). L-, E-, and P-selectin are type-1 membrane glycoproteins sharing a similar structure, comprising an NH2
-terminal calcium-dependent “C type” lectin domain, an EGF-like domain, variable numbers of short consensus repeats do-mains, a single-pass transmembrane-domain, and a cytosolic carboxyl terminal tail. Abundant evidence indicates that selec-tins recognize specific carbohydrate ligands. Extensive studies involving mutagenesis, domain swapping, antibody inhibition, etc., have helped to define the functional domains of the selec-tins. It appears that selectin recognition of carbohydrate ligands involves primarily the amino-terminal C-type lectin main, influenced to a substantial extent by the EGF-like do-main, and to a much lesser degree by the short consensus re-peats (1–20). As with most other adhesion receptors, it is also evident that selectins are signaling molecules. This perspective focuses on one of the most puzzling and controversial aspects of selectin biology—the structure of the natural ligands recog-nized by these receptors.
Mammalian lectin domains typically recognize specific oli-gosaccharide sequences with considerable selectivity, but rela-tively low affinity. Thus, for example, the cation-independent M6P receptor (CI-M6PR) recognizes mannose 6-phosphate a1-2 linked to another mannose (21), CD22 recognizes an a2-6–linked sialic acid residue attached to Galb1-4GlcNAc (22), and the selectins share the ability to recognize the tet-rasaccharide sialyl-Lewisx (SLex)1 and its isomer sialyl-Lewisa.
In the first two instances, Kd values for the basic recognition
sequence are in the low micromolar range, and higher affinity
binding (nanomolar range) is achieved either by multiple bind-ing sites within a sbind-ingle lectin molecule (CI-M6PR) or by mo-lecular aggregation of the monovalent lectin on the cell surface (CD22). This phenomenon of multivalency-based avidity seems to apply to most other naturally occurring lectins (23). With the selectins, the binding affinities for sialyl-Lewisx are very
poor, being in the mid micromolar to millimolar range. How-ever, molecular aggregation (e.g., demonstrable by chemical cross-linking) has not been reported for any of the selectins (regional clustering has been reported for L-selectin on the pseudopods of neutrophils). Instead, there are some reports of high affinity binding of recombinant soluble monovalent selec-tins to natural ligands (16, 17). Thus, the issue of how selecselec-tins generate functional high affinity binding remains unresolved (see discussion below). Regardless, the recombinant selectins used to identify biological ligands are multimeric in structure and/or are usually presented in multivalent clustered arrays on solid supports or in soluble complexes. Thus, it should not be surprising that a large number and variety of molecules have been reported to bind to these multimeric recombinant selec-tins in a glycosylation-dependent manner. To date, very few of these “ligands” have actually been shown to mediate biologi-cal interactions. Thus, the current challenge is to tell the differ-ence between what can bind to a recombinant selectin in vitro, and what does bind in vivo to a cell surface selectin in a biolog-ically relevant manner.
What should be the criteria for a real selectin ligand? First and foremost, it should be present in the right place at the right time; e.g., a true P-selectin ligand should be present on the sur-face of a mature circulating blood cell at a time when P-selec-tin is being actively expressed on an endothelial or platelet sur-face somewhere in the vasculature. Second, selective removal or blockade of the putative ligand on the intact cell should ab-rogate biologically relevant interactions. Next, absence of the ligand should abrogate the function of the relevant selectin in the specific situation in question. Finally, the ligand should be recognized with some selectivity by the specific selectin in question, with a relatively high affinity, and preferably with a well-defined stoichiometry. Of course, some of these criteria might not be fulfilled if other relevant ligands share partial functional redundancy and/or overlap in recognition by other selectins.
Let us consider as an example the potential ligands on the surface of a circulating neutrophil for P-selectin (which is itself expressed on activated endothelium or platelets). A large body of evidence indicates that sugar chains called sialylated fucosyl-ated lactosamines (of which SLex is the simplest example) are
critical components of the ligands (1–14). The relevant
fucosyl-Address correspondence to Ajit Varki, Glycobiology Program, UCSD Cancer Center, and Division of Cellular and Molecular Medi-cine, University of California, San Diego, La Jolla, CA 92093. Phone: 619-534-3296; FAX: 619-534-5611; E-mail: [email protected]
Accepted for publication 3 December 1996.
1. Abbreviations used in this paper: ESL-1, E-selectin ligand–1; HEV, high endothelial venules; PSGL-1, P-selectin glycoprotein ligand-1 SLex, sialyl-Lewisx.
Selectin Ligands: Will the Real Ones Please Stand Up?
Ajit Varki
transferase enzymes have recently been identified and dis-rupted in whole animals (24–27). Since the enzymes involved in SLex synthesis reside in the late part of the Golgi apparatus,
many cell surface glycoproteins isolated from myeloid cells could carry some copies of this structural motif. Thus, it should not be surprising that a large number of neutrophil glycopro-teins (leukosialin, L-selectin, LAMPs, CEA-like proglycopro-teins, LFA-1, etc.) have been reported to act as P-selectin (and/or E-selectin) ligands when purified and presented at high density in various in vitro assays. In contrast, only one quantitatively minor neutrophil glycoconjugate (whose polypeptide back-bone is called P-selectin glycoprotein ligand-1, PSGL-1) (28, 29) actually generates high affinity binding and biologically relevant interactions with P-selectin, by presenting , 1% of the surface SLex (30–32) in conjunction with certain tyrosine
sulfate residues (33–35). This molecule is present in the right place at the right time. It does bind with relative selectivity to P-selectin (although it is also recognized by L- and E-selectin), in a calcium-dependent manner, with a relatively high (nano-molar) affinity and likely with a defined stochiometry. Selec-tive removal by Pasturella hemolytica O-sialoglycoprotease (which cleaves PSGL-1 and only a few other mucin-type glyco-proteins from neutrophil surfaces) abrogates binding (30), and selective blockade by specific monoclonal antibodies (with ap-propriate nonblocking controls) abrogates the physiologically relevant “rolling” of neutrophils on P-selectin–expressing vas-cular endothelium in vivo (36). Likewise, PSGL-1 blockade abrogates P-selectin–mediated biochemical responses among activated platelets and monocytes (15, 37). Thus, the many other SLex-bearing glycoproteins and glycolipids present in
greater abundance on the neutrophil surface seem to be insuf-ficient to provide functional redundancy for PSGL-1. The role of PSGL-1 remains to be confirmed by studying the conse-quences of a genetically determined absence of the polypeptide backbone; i.e., a “knock-out” mouse. Regardless, we can rea-sonably conclude that when correctly glycosylated and tyrosine sulfated, PSGL-1 can present a real P-selectin ligand. In this re-gard, an interesting recent development is that neutrophil PSGL-1 can also act as a true ligand for L-selectin, mediating the phenomenon of neutrophils rolling on other neutrophils that are already adherent to activated endothelium (38–42).
In no other instance has the criteria for a real selectin ligand been completely fulfilled. Those that come the closest are considered below. GlyCAM-1 is a small mucin-type glyco-protein that, when correctly glycosylated and sulfated (on the sugar chain), can be recognized with high affinity and relative specificity by L-selectin (4, 10, 11, 43). It is also expressed in the right place (high endothelial venules, HEV) at the right time (constitutively in lymph nodes and inducibly in inflamed tissues). However, GlyCAM-1 lacks a transmembrane domain and appears to be primarily a secreted molecule. Indeed, mod-ulation of its secretion during immune responses suggests that it is primarily an antiadhesion molecule (44). Of course, since L-selectin is also a signaling molecule, GlyCAM-1 could be li-gating this receptor on the circulating neutrophil cell surface to carry out some other functions. Indeed, soluble GlyCAM-1 has recently been shown to activate b2-integrins (45). A more attractive candidate for an endothelial L-selectin ligand ap-peared to be the mucin-type polypeptide CD34. As with Gly-CAM-1, CD34 can be recognized with high affinity and rela-tive specificity by L-selectin when it is correctly glycosylated and sulfated (4, 10, 11). Furthermore, it is a transmembrane
glycoprotein expressed throughout the endothelial cells of the vasculature (46). However, CD34 only appears to be correctly glycosylated for L-selectin recognition in the HEV of lymph nodes. Moreover, genetic disruption of CD34 expression in mice does not give an obvious loss of lymphocyte trafficking to lymph nodes (47). Other candidates for true L-selectin ligands include the as yet uncloned gp200 of lymph node HEV (4, 11), and the correctly glycosylated and sulfated form of MAd-CAM-1 (12). The latter is a particularly interesting molecule found in Peyer’s patch and mesenteric lymph node HEV, where it can function both as a protein ligand for the integrin a4b7, and/or as a ligand for L-selectin (12, 48).
All of the ligands mentioned above are sialomucins; i.e., they have large numbers of O-linked sugar chains clustered to-gether on the polypeptide backbone. In contrast, a polypep-tide called E-selectin ligand–1 (ESL-1) was discovered by ex-pression cloning and found to carry exclusively N-linked sugar chains, which could constitute a high affinity E-selectin ligand when decorated with sialylated fucosylated lactosamine units such as SLex (9, 49). However, sequence comparisons showed
a strong homology of ESL-1 to a putative chicken fibroblast growth factor receptor (9, 49), and identity to a previously well-known protein marker of the medial Golgi called MG-160 (50). If this internal location holds true in leucocytes, ESL-1 would not be present “at the right place, at the right time.” However, it is possible that this is a matter of cell-type specific regulation that has not yet been elucidated. Another example of a potential selectin ligand with primarily N-linked chains is the heat-stable antigen CD24, which has been reported to bind to P-selectin in vitro (51). It is also noteworthy that E-selectin has been reported to bind with relatively high affinity to cer-tain sialylated polyfucosylated N-linked sugar chains derived from neutrophils, completely independent of any attachment to a polypeptide backbone (52). Likewise, sialylated fucosyl-ated glycolipids from leukocytes can be effective ligands for E-selectin when presented at high density in vitro (53–55). In all of these instances, definitive proof of in vivo function is cur-rently lacking.
Another puzzling fact is that a completely different class of sugar chains called the heparan sulfate glycosaminoglycans (lacking sialic acids or fucose) can also be recognized by L- and P-selectin (56). Calcium dependency and competition studies suggest that the binding site for these sulfated, uronic acid– containing sugar chains is identical to or closely adjacent to those for the sialylated mucin-type ligands (56–58). Although these molecules have not fulfilled all the criteria for a true se-lectin ligand, they are certainly expressed in the right place (i.e., the surface of endothelia and blood cells) and have the potential diversity to generate ligand specificity. Indeed, a re-cent study shows that aortic endothelial heparan sulfates can act as functional ligands for L-selectin (59). In this regard, it is also of interest that the heparan sulfates are closely related in structure to the commonly used intravenous therapeutic agent heparin, which has been assumed to function primarily via binding to antithrombin III (8). It is possible that some of the therapeutic effects of heparin are related to P- and/or L-selec-tin inhibition.
molecules. However, as with the sialylated fucosylated gly-colipids, it is unclear if the binding seen with purified products occurs because of their clustered presentation in various in vitro assays, or if they do indeed serve as high affinity ligands in vivo. Also, not all of these binding phenomena are consis-tently calcium dependent. In this regard, it is of interest that some anionic phospholipids can bind to L- and P-selectin (but not to E-selectin) at a site distinct from the carbohydrate-bind-ing site (18). Indeed, many of the confuscarbohydrate-bind-ing data concerncarbohydrate-bind-ing P-and L-selectin might be explained by a two-site model, with a calcium-dependent site that recognizes sialylated fucosylated components of ligands and a calcium-independent anion-bind-ing site that serves to stabilize the first interaction. Overall, if it is really true that selectins can bind to mucins, heparan sulfate glycosaminoglycans, sulfatides, glycolipids, tyrosine sulfates, or complex N-linked sugar chains in vivo, the matter of defin-ing the biologically relevant ligands assumes a dauntdefin-ing com-plexity. Future studies should focus more upon demonstrating ligand functions in vivo.
Yet another class of potential selectin ligands that should be mentioned are the mucin-type glycoproteins expressed on the cell surface and in the secretions of epithelial carcinomas. Prior evidence for the association of carcinoma mucin sialyla-tion and fucosylasialyla-tion with tumor progression and metastases (62) has led to recent studies asking if selectin recognition is in-volved. While the last word is not in, it is clear that epithelial carcinomas can express mucin-type selectin ligands, and that these may mediate tumor cell interactions with blood cells and endothelia (63–66). In view of the well-known role of platelet and leukocyte interactions with tumor cells in the process of metastases, these “pathological” ligands bear exploration as potentially important determinants.
Another confusing issue is that, despite the selectins show-ing excellent cross-recognition of ligands between species, the ligands themselves may be presented by distinct polypeptide backbones. Thus, human homologues of ESL-1 and GlyCAM-1 have yet to be described, and the same is true of a 250-kD gly-coprotein reported to mediate E-selectin binding to bovine g-d T cells (67). One possible explanation is that the glycosyltrans-ferases that synthesize the carbohydrate components of the ligands are under independent and more severe evolutionary selection pressures (e.g., because of the binding of microbial pathogens to cell surface sugars). Thus, they may be more prone to divergence than the carrier polypeptides themselves. If so, one should be careful in extrapolating conclusions re-garding selectin ligands among different species.
It is very convenient to use the names of the polypeptide backbone when referring to selectin ligands; e.g., “PSGL-1 is the ligand for P-selectin.” However, it is important to remem-ber that unless they are correctly glycosylated and/or other-wise modified (e.g., sulfated), these polypeptides are not ligands. Thus, for example, CD34 is widely expressed on vas-cular endothelia (46) and PSGL-1 is expressed on leukocytes other than neutrophils and monocytes (29, 68, 69); however, these polypeptides do not generate selectin ligands in most of these situations, presumably because they are not correctly modified posttranslationally. Indeed, recent studies indicate that even on neutrophils, only z 20% of the PSGL-1 ex-pressed is capable of binding to P-selectin (R. Cummings, per-sonal communication). Also, as discussed above, binding of some selectin ligands may be completely independent of a polypeptide chain. Thus, these polypeptides are better thought
of as carriers of the true ligands, which are made up of combi-nations of posttranslational modifications such as glycosylation and sulfation.
Since very few mucin-type polypeptides seem to carry high affinity selectin ligands, it was initially thought that these pro-teins might be targets for selective biosynthesis of unique oli-gosaccharide sequences that would explain the high affinity. Indeed, there are well-established examples of polypeptide-specific glycosylation reactions in other systems (70). An un-usual 69-sulfated SLex structure found on GlyCAM-1 (4, 11,
43) was initially thought to be a candidate; however, direct analysis of the chemically synthesized molecule indicates that it is not a particularly potent ligand in comparison with SLex
(71, 72). A more promising candidate may be a relatively un-usual Core 2 branched sialylated polyfucosylated O-linked chain found in a small copy number on PSGL-1 (32); however, this has not yet been directly shown to be essential for P-selec-tin recognition. No other truly unique oligosaccharides have been found attached to mucin-type selectin ligands (66). Thus, the generation of a high affinity ligand seems to require an un-explained combination of the polypeptide backbone and its modifications (glycosylation and/or sulfation). One possible explanation for this paradox, and for the recognition of so many diverse ligands by the same selectin lectin domains, is that they share a common “clustered saccharide patch” or “clustered anionic patch” that can be generated in more ways than one (3). Thus, the common features of the selectin ligands (carboxylate residues and/or sulfate esters, along with hy-droxyl, methyl, or N-acetyl groups) can all be found on a vari-ety of oligosaccharide structures. Appropriate combinations of such units might generate high affinity ligands (3). While this theory can account for many of the existing observations about selectin ligands, it is difficult to prove without having crystal structures of the selectins in complex with several of their ligands for inspection and comparison.
From the title and the content of this perspective, it will be evident to the reader that many more studies are needed to elucidate which are the “real” selectin ligands. While the final answers may be complex, their exploration is very worthwhile. Knowing the precise nature of the high affinity ligands could also aid in pursuing one of the Holy Grails of the selectin field: developing high affinity monospecific selectin inhibitors for therapy of acute and chronic inflammatory reactions and is-chemia-reperfusion injury states. Of course, an alternate way to achieve the same end is the screening of randomized librar-ies composed of defined structural subcomponents. In this re-gard, it is interesting that the highest affinity ligands described to date for selectins are artificial ones that have been isolated by affinity selection from pools of randomized molecules be-longing to yet another well-known category of acidic polysac-charides: single-stranded oligonucleotides (73, 74).
Acknowledgments
The author thanks Shiv Pillai and Nissi Varki for helpful comments, and others for providing unpublished data. Since the current litera-ture on selectins is voluminous, the bibliography presented is repre-sentative rather than fully inclusive.
References
2. Albelda, S.M., C.W. Smith, and P.A. Ward. 1994. Adhesion molecules and inflammatory injury. FASEB J. 8:504–512.
3. Varki, A. 1994. Selectin ligands. Proc. Natl. Acad. Sci. USA. 91:7390–7397. 4. Rosen, S.D., and C.R. Bertozzi. 1994. The selectins and their ligands.
Curr. Opin. Cell Biol. 6:663–673.
5. Springer, T.A. 1995. Traffic signals on endothelium for lymphocyte recir-culation and leukocyte emigration. Annu. Rev. Physiol. 57:827–872.
6. Tedder, T.F., D.A. Steeber, A. Chen, and P. Engel. 1995. The selectins: vascular adhesion molecules. FASEB J. 9:866–873.
7. Furie, B., and B.C. Furie. 1995. The molecular basis of platelet and en-dothelial cell interaction with neutrophils and monocytes: role of P-selectin and the P-selectin ligand, PSGL-1. Thromb. Haemost. 74:224–227.
8. Nelson, R.M., A. Venot, M.P. Bevilacqua, R.J. Linhardt, and I. Stamen-kovic. 1995. Carbohydrate-protein interactions in vascular biology. Annu. Rev. Cell Biol. 11:601–631.
9. Vestweber, D. 1996. Ligand-specificity of the selectins. J. Cell. Biochem.
61:585–591.
10. Lasky, L.A. 1995. Selectin-carbohydrate interactions and the initiation of the inflammatory response. Annu. Rev. Biochem. 64:113–139.
11. Rosen, S.D., and C.R. Bertozzi. 1996. Leukocyte adhesion—two selec-tins converge on sulphate. Curr. Biol. 6:261–264.
12. Butcher, E.C., and L.J. Picker. 1996. Lymphocyte homing and homeo-stasis. Science (Wash. DC). 272:60–66.
13. Kansas, G.S. 1996. Selectins and their ligands: current concepts and con-troversies. Blood. 88:3259–3287.
14. Crocker, P.R., and T. Feizi. 1996. Carbohydrate recognition systems: functional triads in cell–cell interactions. Curr. Opin. Struct. Biol. 6:679–691.
15. Zimmerman, G.A., T.M. McIntyre, and S.M. Prescott. 1996. Adhesion and signaling in vascular cell–cell interactions. J. Clin. Invest. 98:1699–1702.
16. Ushiyama, S., T.M. Laue, K.L. Moore, H.P. Erickson, and R.P. McEver. 1993. Structural and functional characterization of monomeric soluble P-selec-tin and comparison with membrane P-selecP-selec-tin. J. Biol. Chem. 268:15229–15237. 17. Hensley, P., P.J. McDevitt, I. Brooks, J.J. Trill, J.A. Feild, D.E. Mc-Nulty, J.R. Connor, D.E. Griswold, N.V. Kumar, K.D. Kopple, et al. 1994. The soluble form of E-selectin is an asymmetric monomer. Expression, purification, and characterization of the recombinant protein. J. Biol. Chem. 269:23949– 23958.
18. Malhotra, R., N.R. Taylor, and M.I. Bird. 1996. Anionic phospholipids bind to L-selectin (but not E-selectin) at a site distinct from the carbohydrate-binding site. Biochem. J. 314:297–303.
19. Kolbinger, F., J.T. Patton, G. Geisenhoff, A. Aenis, X.H. Li, and A.G. Katopodis. 1996. The carbohydrate-recognition domain of E-selectin is suffi-cient for ligand binding under both static and flow conditions. Biochemistry. 35: 6385–6392.
20. Revelle, B.M., D. Scott, and P.J. Beck. 1996. Single amino acid residues in the E- and P-selectin epidermal growth factor domains can determine carbo-hydrate binding specificity. J. Biol. Chem. 271:16160–16170.
21. Kornfeld, S. 1992. Structure and function of the mannose 6-phosphate/ insulinlike growth factor II receptors. Annu. Rev. Biochem. 61:307–330.
22. Powell, L.D., and A. Varki. 1995. I-type lectins. J. Biol. Chem. 270: 14243–14246.
23. Weis, W.I., and K. Drickamer. 1996. Structural basis of lectin-carbohy-drate recognition. Annu. Rev. Biochem. 65:441–473.
24. Smith, P.L., K.M. Gersten, B. Petryniak, R.J. Kelly, C. Rogers, Y. Nat-suka, J.A. Alford III, E.P. Scheidegger, S. NatNat-suka, and J.B. Lowe. 1996. Ex-pression of the a(1,3)fucosyltransferase Fuc-TVII in lymphoid aggregate high endothelial venules correlates with expression of L-selectin ligands. J. Biol. Chem. 271:8250–8259.
25. Knibbs, R.N., R.A. Craig, S. Natsuka, A. Chang, M. Cameron, J.B. Lowe, and L.M. Stoolman. 1996. The fucosyltransferase FucT-VII regulates E-selectin ligand synthesis in human T cells. J. Cell Biol. 133:911–920.
26. Maly, P., A.D. Thall, B. Petryniak, G.E. Rogers, P.L. Smith, R.M. Marks, R.J. Kelly, K.M. Gersten, G.Y. Cheng, T.L. Saunders, et al. 1996. The
a(1,3)Fucosyltransferase Fuc-TVII controls leukocyte trafficking through an essential role in L-, E-, and P-selectin ligand biosynthesis. Cell. 86:643–653.
27. Wagers, A.J., J.B. Lowe, and G.S. Kansas. 1996. An important role for the al,3 fucosyltransferase, FucT-VII, in leukocyte adhesion to E-selectin.
Blood. 88:2125–2132.
28. Sako, D., X.-J. Chang, K.M. Barone, G. Vachino, H.M. White, G. Shaw, G.M. Veldman, K.M. Bean, T.J. Ahern, B. Furie, et al. 1993. Expression clon-ing of a functional glycoprotein ligand for P-selectin. Cell. 75:1179–1186.
29. Yang, J., J. Galipeau, C.A. Kozak, B.C. Furie, and B. Furie. 1996. Mouse P-selectin glycoprotein ligand-1: molecular cloning, chromosomal local-ization, and expression of a functional P-selectin receptor. Blood. 87:4176–4186. 30. Norgard, K.E., K.L. Moore, S. Diaz, N.L. Stults, S. Ushiyama, R.P. McEver, R.D. Cummings, and A. Varki. 1993. Characterization of a specific ligand for P-selectin on myeloid cells. A minor glycoprotein with sialylated O-linked oli-gosaccharides. J. Biol. Chem. 268:12764–12774.
31. Li, F.G., P.P. Wilkins, S. Crawley, J. Weinstein, R.D. Cummings, and R.P. McEver. 1996. Post-translational modifications of recombinant P-selectin glycoprotein ligand-1 required for binding to P- and E-selectin. J. Biol. Chem.
271:3255–3264.
32. Wilkins, P.P., R.P. McEver, and R.D. Cummings. 1996. Structures of the
O-glycans on P-selectin glycoprotein ligand-1 from HL-60 cells. J. Biol. Chem.
271:18732–18742.
33. Sako, D., K.M. Comess, K.M. Barone, R.T. Camphausen, D.A. Cum-ming, and G.D. Shaw. 1995. A sulfated peptide segment at the amino terminus of PSGL-1 is critical for P-selectin binding. Cell. 83:323–331.
34. Pouyani, T., and B. Seed. 1995. PSGL-1 recognition of P-selectin is con-trolled by a tyrosine sulfation consensus at the PSGL-1 amino terminus. Cell.
83:333–343.
35. Wilkins, P.P., K.L. Moore, R.P. McEver, and R.D. Cummings. 1995. Ty-rosine sulfation of P-selectin glycoprotein ligand-1 is required for high affinity binding to P-selectin. J. Biol. Chem. 270:22677–22680.
36. Norman, K.E., K.L. Moore, R.P. McEver, and K. Ley. 1995. Leukocyte rolling in vivo is mediated by P-selectin glycoprotein ligand-1. Blood. 86:4417– 4421.
37. Weyrich, A.S., T.M. McIntyre, R.P. McEver, S.M. Prescott, and G.A. Zimmerman. 1995. Monocyte tethering by P-selectin regulates monocyte chemotactic protein-1 and tumor necrosis factor-a secretion. Signal integration and NF-kappaB translocation. J. Clin. Invest. 95:2297–2303.
38. Guyer, D.A., K.L. Moore, E.B. Lynam, C.M.G. Schammel, S. Rogelj, R.P. McEver, and L.A. Sklar. 1996. P-selectin glycoprotein ligand-1 (PSGL-1) is a ligand for L-selectin in neutrophil aggregation. Blood. 88:2415–2421.
39. Spertini, O., A.S. Cordey, N. Monai, L. Giuffrè, and M. Schapira. 1996. P-selectin glycoprotein ligand 1 is a ligand for L-selectin on neutrophils, mono-cytes, and CD341 hematopoietic progenitor cells. J. Cell Biol. 135:523–531.
40. Tu, L.L., A.J. Chen, M.D. Delahunty, K.L. Moore, S.R. Watson, R.P. McEver, and T.F. Tedder. 1996. L-selectin binds to P-selectin glycoprotein ligand-1 on leukocytes—interactions between the lectin, epidermal growth fac-tor, and consensus repeat domains of the selectins determine ligand binding specificity. J. Immunol. 157:3995–4004.
41. Fuhlbrigge, R.C., R. Alon, K.D. Puri, J.B. Lowe, and T.A. Springer. 1996. Sialylated, fucosylated ligands for L-selectin expressed on leukocytes me-diate tethering and rolling adhesions in physiologic flow conditions. J. Cell Biol.
135:837–848.
42. Alon, R., R.C. Fuhlbrigge, E.B. Finger, and T.A. Springer. 1996. Inter-actions through L-selectin between leukocytes and adherent leukocytes nucle-ate rolling adhesions on selectins and VCAM-1 in shear flow. J. Cell Biol. 135: 849–865.
43. Hemmerich, S., H. Leffler, and S.D. Rosen. 1995. Structure of the O -gly-cans in GlyCAM-1, an endothelial-derived ligand for L-selectin. J. Biol. Chem.
270:12035–12047.
44. Hoke, D., R.E. Mebius, N. Dybdal, D. Dowbenko, P. Gribling, C. Kyle, S. Baumhueter, and S.R. Watson. 1995. Selective modulation of the expression of L-selectin ligands by an immune response. Curr. Biol. 5:670–678.
45. Hwang, S.T., M.S. Singer, P.A. Giblin, T.A. Yednock, K.B. Bacon, S.I. Si-mon, and S.D. Rosen. 1996. GlyCAM-1, a physiologic ligand for L-selectin, acti-vates b2 integrins on naive peripheral lymphocytes. J. Exp. Med. 184:1343–1348.
46. Baumhueter, S., N. Dybdal, C. Kyle, and L.A. Lasky. 1994. Global vascu-lar expression of murine CD34, a sialomucin-like endothelial ligand for L-selec-tin. Blood. 84:2554–2565.
47. Cheng, J., S. Baumhueter, G. Cacalano, K. Carver-Moore, H. Thi-bodeaux, R. Thomas, H.E. Broxmeyer, S. Cooper, N. Hague, M. Moore, and L.A. Lasky. 1996. Hematopoietic defects in mice lacking the sialomucin CD34.
Blood. 87:479–490.
48. Berg, E.L., L.M. McEvoy, C. Berlin, R.F. Bargatze, and E.C. Butcher. 1993. L-selectin–mediated lymphocyte rolling on MAdCAM-1. Nature (Lond.).
366:695–698.
49. Steegmaier, M., A. Levinovitz, S. Isenmann, E. Borges, M. Lenter, H.P. Kocher, B. Kleuser, and D. Vestweber. 1995. The E-selectin-ligand ESL-1 is a variant of a receptor for fibroblast growth factor. Nature (Lond.). 373:615–620.
50. Gonatas, J.O., Z. Mourelatos, A. Stieber, W.S. Lane, J. Brosius, and N.K. Gonatas. 1995. MG-160, a membrane sialoglycoprotein of the medial cis-ternae of the rat Golgi apparatus, binds basic fibroblast growth factor and ex-hibits a high level of sequence identity to a chicken fibroblast growth factor re-ceptor. J. Cell Sci. 108:457–467.
51. Aigner, S., M. Ruppert, M. Hubbe, M. Sammar, Z. Sthoeger, E.C. Butcher, D. Vestweber, and P. Altevogt. 1995. Heat stable antigen (mouse CD24) supports myeloid cell binding to endothelial and platelet P-selectin. Int. Immunol. 7:1557–1565.
52. Patel, T.P., S.E. Goelz, R.R. Lobb, and R.B. Parekh. 1994. Isolation and characterization of natural protein-associated carbohydrate ligands for E-selec-tin. Biochemistry. 33:14815–14824.
53. Stroud, M.R., K. Handa, M.E.K. Salyan, K. Ito, S.B. Levery, S. Hako-mori, B.B. Reinhold, and V.N. Reinhold. 1996. Monosialogangliosides of hu-man myelogenous leukemia HL60 cells and normal huhu-man leukocytes. 1. Sepa-ration of E-selectin binding from nonbinding gangliosides, and absence of sialosyl-Lex having tetraosyl to octaosyl core. Biochemistry. 35:758–769.
55. Alon, R., T. Feizi, C.-T. Yuen, R.C. Fuhlbrigge, and T.A. Springer. 1995. Glycolipid ligands for selectins support leukocyte tethering and rolling under physiologic flow conditions. J. Immunol. 154:5356–5366.
56. Nelson, R.M., O. Cecconi, W.G. Roberts, A. Aruffo, R.J. Linhardt, and M.P. Bevilacqua. 1993. Heparin oligosaccharides bind L- and P-selectin and in-hibit acute inflammation. Blood. 82:3253–3258.
57. Norgard-Sumnicht, K.E., N.M. Varki, and A. Varki. 1993. Calcium-dependent heparin-like ligands for L-selectin in nonlymphoid endothelial cells.
Science (Wash. DC). 261:480–483.
58. Norgard-Sumnicht, K., and A. Varki. 1995. Endothelial heparan sulfate proteoglycans that bind to L-selectin have glucosamine residues with unsubsti-tuted amino groups. J. Biol. Chem. 270:12012–12024.
59. Giuffre, L., A. Cordey, N. Monai, Y. Tardy, M. Schapira, and O. Sper-tini. 1997. Monocyte adhesion to activated aortic endothelium: role of L-selec-tin and heparan sulfate proteoglycans J.Cell Biol. In press.
60. Aruffo, A., W. Kolanus, G. Walz, P. Fredman, and B. Seed. 1991. CD62/ P-selectin recognition of myeloid and tumor cell sulfatides. Cell. 67:35–44.
61. Needham, L.K., and R.L. Schnaar. 1993. The HNK-1 reactive sulfoglu-curonyl glycolipids are ligands for L-selectin and P-selectin but not E-selectin.
Proc. Natl. Acad. Sci. USA. 90:1359–1363.
62. Kim, Y.S., J. Gum, and I. Brockhausen. 1996. Mucin glycoproteins in neoplasia. Glycoconj. J. 13:693–707.
63. Izumi, Y., Y. Taniuchi, T. Tsuji, C.W. Smith, S. Nakamori, I.J. Fidler, and T. Irimura. 1995. Characterization of human colon carcinoma variant cells selected for sialyl Lex carbohydrate antigen: liver colonization and adhesion to
vascular endothelial cells. Exp. Cell Res. 216:215–221.
64. Mannori, G., P. Crottet, O. Cecconi, K. Hanasaki, A. Aruffo, R. M. Nel-son, A. Varki, and M.P. Bevilacqua. 1995. Differential colon cancer cell adhe-sion to E-, P-, and L-selectin: role of mucin type glycoproteins. Cancer Res. 55: 4425–4431.
65. Majuri, M.L., R. Niemelä, S. Tiisala, O. Renkonen, and R. Renkonen. 1995. Expression and function of a2,3-sialyl- and a1,3/1,4-fucosyltransferases in colon adenocarcinoma cell lines: role in synthesis of E-selectin counter-recep-tors. Int. J. Cancer. 63:551–559.
66. Crottet, P., Y.J. Kim, and A. Varki. 1996. Subsets of sialylated, sulfated mucins of diverse origins are recognized by L-selectin. Lack of evidence for unique oligosaccharide sequences mediating binding. Glycobiology. 6:191–208.
67. Walcheck, B., G. Watts, and M.A. Jutila. 1993. Bovine gamma/delta T cells bind E-selectin via a novel glycoprotein receptor: first characterization of a lymphocyte/E-selectin interaction in an animal model. J. Exp. Med. 178:853– 863.
68. Vachino, G., X.J. Chang, G.M. Veldman, R. Kumar, D. Sako, L.A. Fouser, M.C. Berndt, and D.A. Cumming. 1995. P-selectin glycoprotein ligand-1 is the major counter-receptor for P-selectin on stimulated T cells and is widely distributed in non-functional form on many lymphocytic cells. J. Biol. Chem.
270:21966–21974.
69. Laszik, Z., P.J. Jansen, R.D. Cummings, T.F. Tedder, R.P. McEver, and K.L. Moore. 1996. P-selectin glycoprotein ligand-1 is broadly expressed in cells of myeloid, lymphoid, and dendritic lineage and in some nonhematopoietic cells. Blood. 88:3010–3021.
70. Baenziger, J.U. 1994. Protein-specific glycosyltransferases: how and why they do it. FASEB J. 8:1019–1025.
71. Tsuboi, S., Y. Isogai, N. Hada, J.K. King, O. Hindsgaul, and M. Fukuda. 1996. 69-sulfo sialyl Lex but not 6-sulfo sialyl Lex expressed on the cell surface
supports L-selectin–mediated adhesion. J. Biol. Chem. 271:27213–27216. 72. Koenig, A., R. Jain, R. Vig, K. Norgard-Sumnicht, K.L. Matta, and A. Varki. 1997. Selectin inhibition. Synthesis and evaluation of novel sialylated, sulfated and fucosylated oligosaccharides, including the major capping group of GlyCAM-1. Glycobiology. In press.
73. O’Connell, D., A. Koenig, S. Jennings, B. Hicke, H.L. Han, T. Fitzwa-ter, Y.F. Chang, N. Varki, D. Parma, and A. Varki. 1996. Calcium-dependent oligonucleotide antagonists specific for L-selectin. Proc. Natl. Acad. Sci. USA.
93:5883–5887.
74. Hicke, B.J., S.R. Watson, A. Koenig, C.K. Lynott, R.F. Bargatze, Y.-F. Chang, S. Ringquist, L. Moon-McDermott, S. Jennings, T. Fitzwater, et al. DNA aptamers block L-selectin function in vivo: inhibition of human lympho-cyte trafficking in SCID mice. J. Clin. Invest. 98:2688–2692.
“Cell Adhesion In Vascular Biology”
Series Editors, Mark H. Ginsberg, Zaverio M. Ruggeri, and Ajit P. Varki
October 15, 1996 Adhesion and signaling in vascular cell–cell interactions ...Guy Zimmerman, Tom McIntyre, and
...Stephen Prescott
November 1, 1996 Endothelial adherens junctions: implications in the control of vascular
permeability and angiogenesis ...Elisabetta Dejana
November 15, 1996 Genetic manipulation of vascular adhesion molecules in mice ... Richard O. Hynes and Denisa D. Wagner
December 1, 1996 The extracellular matrix as a cell cycle control element in
atherosclerosis and restenosis ...Richard K. Assoian and ...Eugene E. Marcantonio
December 15, 1996 Effects of fluid dynamic forces on vascular cell adhesion ...Konstantinos Konstantopoulos and
...Larry V. McIntire January 1, 1997 The biology of PECAM-1 ...Peter J. Newman January 15, 1997 Selectin ligands: will the real ones please stand up? ...Ajit Varki February 1, 1997 Cell adhesion and angiogenesis...Joyce Bischoff
February 15, 1997 New advances in von Willebrand Factor biology...Zaverio Ruggeri
March 1, 1997 Therapeutic inhibition of carbohydrate-protein interactions in vivo...John Lowe and Peter Ward
March 15, 1997 Integrins and vascular matrix assembly ...Erkki Ruoslahti
April 1, 1997 Platelet GPIIb/IIIa antagonists: the first anti-integrin receptor therapeutics...Barry Coller
April 15, 1997 Importance of shear stress in endothelial adhesion molecule expression ...Michael Gimbrone
May 1, 1997 Proteoglycans and proteoglycan-binding proteins in vascular biology ...Robert Rosenberg
May 15, 1997 New insights into integrin-ligand interaction ...Robert Liddington and Joseph Loftus
June 1, 1997 Adhesive interactions of Sickle erythrocytes with endothelium ...Robert Hebbel
June 15, 1997 Cell migration in vascular biology ...Stephen Schwartz
July 1, 1997 Integrin signaling in vascular biology...Sanford Shattil and Mark Ginsberg
July 15, 1997 Multi-step mechanisms of leukocyte homing...Eugene Butcher
